The present invention relates to an antenna which is to be mounted on a vehicle, and which is provided with an improved waterproof structure with respect to a circuit board arranged in a base member of the antenna.
An example of the structure of a related-art antenna will be described below with reference to FIGS. 5 and 6. In an upper part of an approximately hat-shaped case 10, a base end of an antenna section 12 is arranged in a pivotable manner. A base member 14 is fixed to a lower end opening face of the case 10 by a screw or the like. A circuit board 16 and the like are arranged in a space formed by the case 10 and the base member 14. A screw 14a protruding in a bottom surface of the base member 14 is inserted into a hole 18a drilled in the vehicle body 18. A nut which is not shown is engaged from the inside of the vehicle body 18, so that the base member 14 is fixed to the vehicle body 18.
A pad 20 having elasticity is inserted between the base member 14 and the vehicle body 18. In the pad 20, a pad lip 20a is provided that surrounds the entire periphery of the hole 18a and that protrudes toward the vehicle body 18. When the base member 14 is fixed to the vehicle body 18, the pad lip 20a is damped and elastically deformed so as to come close contact with the vehicle body 18. This prevents rain water or the like from entering into the vehicle body 18 through the hole 18a. Further, at a lower end edge of the case 10, a case lip 10a protruding downward and coming contact with the pad 20 is provided as shown in FIG. 6. When the base member 14 is fixed to the vehicle body 18, the case lip 10a comes elastic firm contact with the elastic pad 20, so that a watertight structure is formed between the case 10 and the pad 20. This prevents rain water from entering into the case 10, and hence protects the circuit board 16 arranged in the inner space from being exposed to the rain water.
In the above structure, in order to ensure the watertight structure between the case 10 and the pad 20, the case lip 10 must be brought into contact with the pad 20 firmly. Thus, for the purpose of reinforcement of the pad 20, a reinforcement lip 20b is provided on the pad 20 in the side facing the vehicle body 18 and at a position opposing to the case lip 10a as shown in FIG. 6. The reinforcement lip 20b has a size approximately corresponding to the size of the lower end edge of the case 10. Meanwhile, in general, the vehicle body 18 is composed of gradual complicated curved surfaces. Thus, when the reinforcement lip 20b is brought into firm contact with such a vehicle body 18 in a large area, the curved surface of the vehicle body 18 would be deformed undesirably. Thus, the pad 20 has to be designed separately for each type of vehicle body 18 in order to avoid deformation in the curved surface. Nevertheless, separate fabrication of the pad 20 for each vehicle body type is not economical.
Japanese Patent Publication No. 10-84207A also discloses an antenna to be mounted on a vehicle body. In this antenna, a ring-shaped ridge for covering the lower end periphery of the case is provided in the outer periphery of the pad. When the ring-shaped ridge covers the lower end periphery of the case, a watertight structure is formed between the case and the pad.
However, when the pad deforms elastically in correspondence to the curved surface of a vehicle body, the ring-shaped ridge also deforms. Since a pad is brought into elastic contact with a lower end periphery of the case solely by virtue of the elasticity of a ring-shaped ridge of the pad, the above deformation causes a change in the elasticity for establishing elastic contact with the lower end periphery of the case, and thereby may cause insufficient reliability in the watertight structure. Thus, also in this configuration, the pad needs to be fabricated separately for each vehicle body type.